Cooking utensil with bottom wall adapted for induction heating

ABSTRACT

A cooking utensil with bottom wall adapted for induction heating, is provided. The cooking utensil includes a container made from a first material that has attached to the outside of its bottom wall a heat distributing plate made from a second, different, heat conducting material, the outer surface having a series of spaced projections with the heat distributing plate being made up of a disc produced from ferromagnetic material provided with a number of perforations equivalent to the number of projections and appropriately distributed to allow the engagement of the disc, backed onto the bottom wall, by inserting the projections through the perforations, leaving the disc joined to the bottom wall by riveting the projections.

This application is a U.S. National Phase Application of PCTInternational Application No. PCT/ES2003/000459 filed Sep. 11, 2003.

FIELD OF THE INVENTION

This invention relates to a cooking utensil, particularly a cookingcontainer such as a saucepan, pan or pot, with a bottom wall adapted foran induction cooker.

BACKGROUND

It is known that although metallic containers, such as those obtainedfor example by aluminium injection casting technology, maintain theirfunctional nature for different types of heat transmission and areparticularly suitable for electric, gas or glass ceramic cookers wherethe heat for the container is produced respectively through directcontact with an electric resistance, with the flame produced by gascombustion or via a special glass ceramic surface, they are not suitablefor induction cookers where the heat for the utensil is produced bytaking advantage of the phenomenon of magnetic induction, where amagnetic field of variable intensity heats ferric materials that arewithin its reach.

Therefore it is necessary to either manufacture the whole utensil in aferromagnetic material with the disadvantages and limitations thisinvolves (cost, weight and handling, heat resistance and durability,etc.), or attach to the bottom wall of the utensil, at least one plateof ferromagnetic material capable of absorbing an efficient yield ofcalorific energy produced by electromagnetic induction because theso-called losses through hysteresis are transformed into calorificenergy.

Different solutions are known in the art, which aim at integrating aferromagnetic plate underneath the bottom wall of a cooking containermade from a different material, for example, an austenitic steel oraluminium.

In this sense the following patents can be quoted. Patent ES-A-2002980proposes a cooking container on the bottom wall of which an intermediateheat diffusing metal plate is attached and underneath said plate aferromagnetic stainless steel lining, with the elements being weldedtogether. Patent ES-A-2108284 describes a culinary utensil with a heatconducting bottom wall having a perforated metallic sheet attached tothe outer face of said bottom wall during casting, using the flow ofmetal to fill said perforations. Patent ES-A-2135632 proposes a cookingutensil with a metallic plate or strip that has openings which receivefiller parts made from a ferromagnetic material, the ensemble beingjoined together by a weld bead applied with a laser beam to the bottomwall of a container made from austenitic steel. Patent applicationDE-A-3713660 describes a cooking utensil made from cast-mouldedaluminium, preferably a saucepan, that includes at least one solidmetallic part attached to the outer part of its bottom wall in thecast-moulding process with the aluminium. Patent application EP-A-722688describes a culinary utensil with a part attached by a high temperaturepressure to the outer face of its bottom wall. Patent applicationWO-A-97/09136 describes a method for manufacturing a piece of metalintended to constitute the bottom wall of a cooking utensil, obtained byroll forging, plastically deforming the metal, and in whichmanufacturing process, one variant thereof envisages the inclusion ofsome metal parts that can be induction heated integrated with the metalpart in the forging process.

SUMMARY OF THE INVENTION

In relation to the afore-mentioned prior art, the present inventionprovides an embodiment which achieves a very firm and stable jointagainst the dilatations and/or deformations that appear, at the bottomwall level, between a ferromagnetic plate and the bottom wall of analuminium cooking utensil on whose outer face the former is attached. Inparticular and by providing a simple union consisting of only saidferromagnetic plate and said bottom wall, there is a reduction in thedamaging effects caused by the heat from the most widely used heatingmeans in the event that said bottom wall comprises various layers ofmaterials of different composition, as in most of the afore-mentionedprior art. With respect to the joining systems used in the actualcasting process, the constitution of the utensil herein proposedrepresents an important simplification of the manufacturing means and,therefore, a significant saving in costs.

According to an exemplary embodiment of the present invention, theproposed cooking utensil is of the type that comprises a container madefrom a first material that has integrated on its bottom wall and on itsouter face, a heat distributing or diffusing plate made from a second,different, heat conducting material, said outer face of the bottom wallof the container having a series of projections (of different shapes) orlugs advantageously placed equidistantly with said heat distributingplate being made up of a disc produced from a ferromagnetic material andhaving a number of perforations or holes equivalent to the number ofprojections or lugs and distributed appropriately to allow theengagement of said disc, backed onto said bottom wall, by means of thecorrespondence and insertion of said projections with and through saidholes, leaving the disc joined to the bottom wall by riveting saidprojections, subsequently polishing the outer surface of the disc or theutensil support base.

In a preferred embodiment of the invention the container is to be madefrom aluminium obtained via an injection casting process.

Said disc will be preferably a sheet of stainless steel so that a light,manageable cooking utensil is obtained, suitable for all kinds of heatsources, particularly, an induction cooker.

According to an example of how the invention is implemented, once saidstainless steel disc is fitted into the holes a pressing operation isperformed, acting on one side on the bottom wall and on the other on thevisible face of the disc, with a pressure of considerable magnitudeaccording to the type of utensil and, for example, of the order of aboutan 80 to 110 Tn load whereby the aluminium material of the projectionsor lugs expands and is completely imprisoned in and on the discmaterial, acting as riveting. In this way, a very efficient joint isachieved between the aluminium element (container) and the heatdiffusing ferromagnetic element, which is suitable for cooperating withinduction-produced energy and is very stable against heat dilatations inview of the deformation imposed by the aluminium material on the wallsof the through holes of the ferromagnetic disc and the deformationproper of the lugs, which widens their section thus allowing saidthermal dilatations generated through usage to be subsequently absorbed.

The polishing of the outer face of said disc acting as diffuser providesa suitable finish to the utensil support surface.

In a preferred embodiment of the invention it is envisaged that thecontainer includes an annular partition which surrounds the outersurface of its bottom wall plane defining a flattened housing suitablefor receiving said fitted ferromagnetic heat receiving and diffusingdisc, the height of the partition being slightly lower than that of saidprojections or lugs and leaving the ferromagnetic disc, once attachedthrough pressing and once the lugs are inserted in the holes andriveted, substantially coplanar to the edge of said partition.

The design and positioning of said projections or lugs is such that itallows the two parts, that is, the bottom wall of the aluminiumcontainer and stainless steel disc to remain joined together withoutplay although very high temperatures are reached and in spite of thefact that the aluminium and steel dilate differently.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will become clearafter reading the examples for implementing the invention which aredescribed below with reference to the sheets of drawings, in which:

FIG. 1 is an elevation view, partially in section, of the bottom wall ofa cooking utensil according to the invention, before a ferromagneticheat diffusing plate or disc is attached thereto, with the presence of aseries of projections being noticeable, in this case in the form of lugson the outer plane of the bottom wall of the utensil.

FIG. 2 is a plan view of said diffuser disc,

FIGS. 3, 4 and 5 are respective sections along the lines I-I, II-II andIII-III of various lugs on the bottom wall shown in FIG. 1.

FIGS. 6 and 7 illustrate the situation prior to mounting the diffuserdisc and the situation after attaching it to the said bottom wall.

FIG. 8 is an enlarged detail of the diffuser disc adopts before theriveting operation using a suitable pressing machine, and

FIG. 9 illustrates the final situation following the pressing andpolishing operation which provides a riveted join between the twoelements, container and disc, and a flat, regular finish to the utensilsupport plane.

FIGS. 10 and 11 show another cooking utensil and heating energy receiverand diffuser disc ensemble, both with a different number of lugs andperforations, in the situation prior to joining both elements.

FIG. 12 illustrates an example of a projection shaped and distributeddifferently to the lugs illustrated in previous figures.

DETAILED DESCRIPTION OF THE INVENTION

According to these figures, the proposed cooking utensil comprises acontainer 10, such as a saucepan, pan, pot or the like, made from afirst material such as aluminium which provides manageability and alight weight, said container having integrated on the outer face of itsbottom wall a heat distributing or diffusing plate, made up of astainless steel disc 11 or strip. According to the invention, the outersurface 12 of the bottom wall of the container 10 has a series ofdistanced projections or lugs 13 and said stainless steel disc 11 has aseries of perforations 14 equivalent to the number of lugs 13appropriately distributed to allow the engagement of said disc 11 backedonto the outer face of said bottom wall, by inserting the lugs 13through the holes 14, leaving the disc 11 joined to the bottom wall byriveting the lugs 13 with a pressing operation that acts on one side onthe bottom wall of the container 10 and on the other side on the disc11, and then applying a polishing or grinding operation to the outersurface of the disc 11 which will form the utensil support base.

The said pressing operation shall be carried out advantageously using ahydraulic press provided with a suitable set of handling elements forpositioning, attaching and riveting the bottom wall and disc ensembleautomatically, such as a transfer machine which is not shown, havingpositioning stations for both elements, that is, the bottom wall of theutensil and the disc joined together, a station for checking theposition of the diffuser disc, a hydraulic riveting station and anautomatic discharge station.

In FIG. 6 it can be seen that the bottom wall of the container 10 has anannular partition 15 which surrounds the outer surface of its bottomplane defining an open, flattened housing 16, suitable for receivingsaid fitted diffuser disc 11, the height of said partition 15 beingslightly lower than that of said lugs 13 so that the disc 11, once it isattached and the lugs 13 are inserted into the holes 14, is coplanar tothe edge of said partition 15 as can be seen in FIG. 9.

In a preferred embodiment of the invention and as can be seen in FIGS. 3and 5 said lugs have a frustoconical shape and they are distributedaccording to various concentric circumferential alignments. Generally,the lugs 13 belonging to different alignments will have a differentthickness and likewise the holes 14 provided for their passage throughthe disc 11 will be adequately sized. In this way, the material stressarising from the thermal dilatations are different in different areas,thereby improving stability.

FIG. 12 illustrates another shape and distribution format for theprojections 13.

According to a preferred way of implementing this model the container 10is to be made from aluminium obtained by injection casting and saiddiffuser disc 11 backed onto the outer surface of its bottom wall ismade from stainless steel.

Having described this invention sufficiently for it to be put intopractice by a person skilled in the art, it is requested that its scopeof protection be extended to those amendments to detail such as thethickness of the ferromagnetic disc, the shape of the projections orlugs and their distribution, the height of the peripheral partition, thepressing strength, the material used and the characteristics of thepresses used, which do not alter the essence of the invention describedin the following claims.

1. A cooking utensil with a bottom wall adapted for induction heating ofthe type comprising: a container made from a first material, that hasintegrated on the outer face of its bottom wall a heat distributing ordiffusing plate made from a second, different, heat conducting material,the outer surface of the bottom wall of the container having a series ofspaced projections and said heat distributing plate comprises a discmade from a ferromagnetic material provided with a number ofperforations equivalent to the number of projections or lugs andappropriately distributed to allow the engagement of said disc, backedonto said bottom wall, by inserting the lugs through the perforations,leaving the disc attached to the bottom wall by riveting saidprojections; and an annular partition which surrounds said outer surfaceof its bottom wall plane defining an open, flattened housing suitablefor receiving said fitted disc, the height of the partition beingslightly lower than that of said lugs and leaving the disc, once it isattached and the lugs are inserted into the holes and riveted, coplanarto the edge of said partition.
 2. The cooking utensil according to claim1, wherein said projections comprise frustoconical lugs.
 3. The cookingutensil according to claim 2, wherein said lugs are distributedaccording to various concentric circumferential alignments, with atleast the lugs belonging to two of said alignments having a differentthickness.
 4. The cooking utensil according to claim 3, wherein saidcontainer is made from aluminium obtained from injection casting andsaid disc backed onto the outer surface of its bottom wall is made fromstainless steel.
 5. The cooking utensil according to claim 4, whereinsaid container forms a saucepan.
 6. The cooking utensil according toclaim 5, wherein said container forms a pot.
 7. The cooking utensilaccording to claim 2, wherein said container is made from aluminiumobtained from injection casting and said disc backed onto the outersurface of its bottom wall is made from stainless steel.
 8. The cookingutensil according to claim 7, wherein said container forms a saucepan.9. The cooking utensil according to claim 8, wherein said containerforms a pot.
 10. The cooking utensil according to claim 1 wherein saidcontainer is made from aluminium obtained from injection casting andsaid disc backed onto the outer surface of its bottom wall is made fromstainless steel.
 11. The cooking utensil according to claim 10, whereinsaid container forms a saucepan.
 12. The cooking utensil according toclaim 11, wherein said container forms a pot.
 13. The cooking utensilaccording to claim 1, further comprising a polished or grounded finishapplied to the outer surface of the disc or utensil support base, oncethe plate or disc has been attached.
 14. The cooking utensil accordingto claim 1, wherein said container is made from aluminium obtained frominjection casting and said disc backed onto the outer surface of itsbottom wall is made from stainless steel.
 15. The cooking utensilaccording to claim 14, wherein said container forms a saucepan.
 16. Thecooking utensil according to claim 15, wherein said container forms apot.
 17. A cooking utensil with a bottom wall adapted for inductionheating comprising: a container made from a first material, that hasintegrated on the outer face of its bottom wall, a heat distributing ordiffusing plate made from a second, different, heat conducting material,wherein the outer surface of the bottom wall of the container has aseries of spaced projections and said heat distributing plate is made upof a disc made from a ferromagnetic material provided with a number ofthrough perforations equivalent to the number of projections andappropriately distributed to allow the engagement of said disc, backedonto said bottom wall, by inserting the lugs through the perforations,the disc remaining attached to the bottom wall by riveting of saidprojections, wherein the projections are comprised of lugs that arefrustoconical before being riveted and that are deformed against thewalls of the through perforations after being riveted, and the cookingutensil comprises a polished or ground finish applied to the outersurface of the cooking utensil support base once the heat distributingplate or disc has been attached to the container.
 18. A method of makinga cooking utensil for use with induction heating comprising: providing acontainer formed from a first material and having a plurality ofprojections comprising frustoconical lugs extending from a surface ofsaid container; providing a diffusion plate formed from a secondmaterial different than said first material; forming a plurality ofthrough perforations in said diffusion plate; receiving said pluralityof projections into said plurality of through perforations; couplingsaid container to said diffusion plate by deforming at least a portionof said plurality of projections against said diffusion plate andagainst the walls of the through perforations; and applying a polishedor ground finish to the outer surface of the utensil support base oncethe plate or disc has been attached to the container.